The use of disks for data storage is universal in the computer industry. Data can be stored on both sides of a disk in concentric recording tracks. To transfer data to and from a spinning disk during high performance read/write operations, at least one transducer is typically situated within micro inches of a surface of the disk. To accommodate such positioning, the transducer is affixed to a specially designed platform connected to an actuator. The platform is aerodynamically designed to fly adjacent to the recording media surface on a thin cushion of ambient air or gas that is created by the spinning disk. The air cushion serves to define the clearance between the transducer (hereinafter referred to as a head) and the spinning disk.
Increased head stability minimizes the likelihood of destructive contact between the head and disk, allowing the head to fly closer to the disk surface. As head/disk clearance is decreased, the density of data stored on the disk can be increased.
The head is typically connected to the actuator by some type of flexible linkage or gimbal (flexure) which allows the head to move in roll, pitch and yaw directions relative to the disk to maintain a relatively parallel relationship to the disk surface.
The flexure is typically connected to the actuator by a generally flat, longitudinal arm portion which is rotated or stroked by the actuator parallel to the surface of the disk thereby positioning the head to a target data transfer (read/write) location under control of servomotor and electronic means. The flexure and arm are configured to provide a spring force to maintain the head a proper distance from the disk under normal spinning conditions.
Designers of disk storage systems have historically been concerned with head to disk contact, either that due to start/stop operation or that caused by physical shock, vibration or acceleration. During normal operation, the thin fluid film between the spinning disk and the flying head provides a margin of safety. However, during initial startup, shut down or power loss, when the disk is not spinning at high speed, the fluid cushion disappears and the spring force of the flexure and arm urges the head to contact the disk directly. This may cause soft or hard data loss, particulate generation and catastrophic damage.
Attempted solutions to the aforementioned limitations include: protective disk coatings, head parking systems that maintain the head in contact with the disk in the power off condition at some dedicated disk area near the hub or perimeter, and/or head unloading systems to physically prevent or reduce the possibility of head-disk contact during non-operation. Disk storage systems without head unloading/loading mechanisms also have to deal with the additional start up torque required to overcome stiction between highly polished read/write heads and the exceedingly smooth disks of modern disk storage systems.
Head loading/unloading systems typically take the form of dynamic loading systems in which disks are brought up to speed or slowed down with the heads in some relatively remote position horizontally, vertically or both, until an air cushion develops. The heads are subsequently guided or positioned in normal vertical relationship to the surface of the disk.
Another area of concern, for disk storage system design, is the aspect of securing the heads after they have been separated from the disks. The following discussion reviews representative proposed mechanisms for loading/unloading and securing heads with discussion of individual benefits and disadvantages.
Day, in patent '431, shows a circumferential flange positioned between oppositely facing magnetic heads to minimize head slap caused by forces parallel to the disk spindle when the heads are in a parked position near the hub. The heads are not positively restrained but are still free to contact the surface of the disks, and the thickness of the flange requires additional spacing be allocated between the disks, thereby decreasing the possible storage density of multi-disk data storage systems.
Jabbari, in patent '260, discloses a staggered ramp assembly, which lowers the torque required for unloading the heads from the disks by separating the ramps for multiple heads into two groups. The inclined sections of the first group of ramps are contacted by a first group of heads, thereby lowering the torque required for lifting the first group of heads by about 2 of that if all heads were lifted at once. After the first group of heads are lifted from the respective disks and the first heads are riding on first ramp flat sections parallel to the disk surfaces, the torque decreases to a lower constant value, resulting from the spring force of the load beams and the friction of the first ramp flat section.
With further outward rotation of the heads, the second group of heads contacts the inclined sections of the outward-staggered ramps and is similarly lifted from the adjacent disks. Jabbari shows a graph comparing the lower torque requirement of the staggered ramps and discusses the decreased power requirements produced by lower torque. However, the lower torque is accompanied by an increased displacement, which is not discussed. Since mechanical work is the product of force times distance, the total energy required to lift both sets of heads then will be about the same as before. The staggered ramps also require an increased radial spacing bed allocated to accommodate the outward staggered ramps, therefore more disk surface must be dedicated to lifting the heads from the disks, thereby wasting possible data storage surface, and decreasing potential storage density.
Patent '481, by Kamo mentions a removable disk cartridge assembly having a ramp loading mechanism for holding the head or heads, with the ramp positioned outside the periphery of the disk when disengaged. Kamo provides no drawings, description or detail on the method or structure of the ramp loading mechanism.
Schmitz, in patent '837 describes a head assembly 136, a fixed ramp loading mechanism 134, and a magnetic actuator latching system 122-124 used with a dual disk and four-head magnetic drive 100. A pin 114 projecting from a rearward extending end of the actuator 116 magnetically latches with either an inner 122 or an outer 123 recessed circumferential latching surface provided on a magnet plate 123. Latching is provided by means of a lowered permanence path including the pin 114, the plate 124 and the associated voice coil motor magnets 118, 119 and either of surfaces 122 or 123, when the actuator is at one or the other extreme angular position. The pin 114 and associated latching surfaces provide a means of holding the actuator 116 magnetically fixed when the drive 100 is deactivated or powered down. The pin 114 and/or plate 124 may be permanent magnets or have residual magnetism such that attractive magnetic forces will hold the pin 114 against either latching surface 122 or 123 without actively driving current through magnetic holding coils so that the actuator arm is prevented from wandering and exposing the disks and heads to possible damage due to physical shocks.
Although not discussed by Schmitz, it is known that a force is required to move the actuator arm from a latched position when the drive is to be activated. Typically, the force to move the arm from the latched position will come from the actuator coil, in this case coil 120. Therefore, the coil 120 must be able to exert enough force to overcome the attractive force holding the pin 114 against surfaces 112, 123. Since the magnitude of the attractive force is directly related to the amount of resistance to physical shock which the drive can sustain, the coil removing force required will similarly scale upwards as this resistance is increased. Increased resistance to shock damage therefore translates into increased power, size and weight demands on the design of such a magnetically latched drive, including the drive electronics. This becomes increasingly problematic for small, portable drives where the coil size and strength and battery capacity is limited, or for drives with many disks having many actuators.
Another consideration for magnetically captured arm/head configurations is controlling the motion of the arm/head once the pin 114 pulls free from the latched position. The torsion applied to the pin and the arm assembly may store elastic energy in the assembly. The large force required to free the arm from its magnetically latched position may cause the arm to jerk free and swing rapidly toward the active disk area. Such a jerk can initiate oscillations in the arm and head due to the resonance of the long cantilever arm, the flexure, and the head suspended therefrom. Such oscillations could result in an edge or corner of the head contacting and damaging the disk surface before the arm can be brought under control.
Another problematic aspect of magnetically latched configurations is the influence of the magnetic latch surfaces on the positioning characteristics of the arm assembly. When the arm approaches an extreme position close to the latch surface, although not close enough to be latched, the arm may still be attracted by the magnetic field and therefore non-uniformly influence the torque-position characteristic of the arm. Additional software or hardware must be added to the data storage system in such cases to compensate for the non-uniform characteristics.
Schmitz also describes a physically fixed unloading ramp structure for receiving the heads in a lifted position when the arm is latched. The ramp structure includes fixed ramps for each head, each fixed ramp overlapping a portion of the outer perimeter of the respective disk. Since the ramps overlay a portion of the disk perimeter, additional space between adjacent disks must be provided. This is a disadvantage for achieving increase data storage density for multi-disk storage systems.
Matsumoto describes another ramp loading and latching mechanism in patent '695. An actuator assembly 25 rotatably mounted on shaft 10 includes head arms 26 corresponding in number to magnetic disks 24. A voice coil 27 on the opposite side of head arm 26 from the shaft 10 rotatably drives the assembly 25. Each of the head arms 26 have one or more spring arms 28 extending therefrom, to each of which are mounted at adjacent distal ends, a corresponding magnetic head 29 for reading and writing to data tracks of each side of a respective disk 24 as the heads 29 are positioned to a particular track. At the center of one side of each head 29 there is formed a protrusion 30 for latching with a corresponding recess 46 provided on one end of a corresponding unloading ramp member 12. Each ramp member 12 is circumferentially mounted on a respective cylindrical boss 41 carried on a bearing 44. The bearing 44 is rotatably mounted on a pin 40. The pin 40 is fixed to the same base 21 supporting the disks 24 and arms 26. The ramp member 12 is comprised of first and second ramp arms 42 and 43 projecting from the boss 41 in planes parallel to the respective disk.
The arms 42 and 43 are disposed in a V-shape so that a rounded distal end of arm 43 makes abutting line contact with an outer surface of a corresponding head arm 26 when the head 29 and arm 26 is swung sufficiently outward from the center of the disks 24. The V-shape of the arms 42, 43 is arranged so that a slant ramp face 45 on the distal end of arm 42 will come into sliding contact with a respective under side of the associated spring arm 28 thereby lifting the head 29 away from the disk 24 read/write surface as the head arm 26 urges the second arm 43 away from the disks and urges first arm 42 toward the disks about the rotatable axis provided by pin 12. Such rotation continues until the protrusion 30 is engaged with the recess 46.
In this position, the heads 29 are safely separated from the disks 24 read/write surfaces. Suitable springs and stops position the ramp face 45 and the distal end of arm 43 so that the latching and unloading functions do not interfere with the normal operation of the read and write functions of the disk drive.
Provision is made for actuating such separation in case of power loss by utilizing the back EMF of the spindle motor, in the conventional manner. Unloading may also be actuated deliberately by suitable electronic command when preparing for moving or shipping the disk drive.
Again, no discussion is presented of the force necessary to disengage the protrusion 30 from recess 46 in order to move the head 29 from the latched position. No accounting is made of design limitations imposed by the power demands of the coil 29 (increased amp-turns product, increased coil resistance and consequent voltage requirements, etc.) and magnet assembly or the increased energy drain from the supply. In addition, over time the friction of the protrusion 30 sliding in and out of recess 46 may generate problematic particulate matter, which could cause catastrophic data loss.
The structure of '695 provides a semi-positive stop for the latching of the head 29 by the cooperation of spring arm 28, protrusion 30, recess 46, and arms 42, 43. However, the shock resistance of the protrusion 30, recess 46, and spring arm 28 will depend on the relative dimensions and spring force provided. In order to meet severe shock requirements, dimensions and/or spring forces will scale with shock requirements. An increased force is thus required to release the protrusion 30 from engagement with recess 46 under spring force from arm 28. High shock resistance will necessitate increasingly powerful actuator coils, magnets and/or larger and heavier components and greater current drain from limited battery supplies. Even so, under sufficient shock the head 29 can still be jarred loose and potentially destroy data on the disk 24.
Additionally, since a portion of the arms 42 and 43 pass over the perimeter of the disks 24 in order to contact the actuator arm 26, additional spacing between adjacent disks must be provided to accommodate the thickness of the arms 42 and 43. Again, this presents a disadvantage for achieving high data storage density.
Morehouse et al., in patent '549 describes a ramp loading and latching system for a multiple disk storage system using fixed ramp-type cam assemblies 42. Morehouse includes an inclined inner ramp face 250 and outer ramp face 254 engaging in portions of associated load beam 224 for loading and unloading heads 230 connected thereto from read/write flying relationship with disks 222. The load beams 224 are part of the actuator assembly 220, which includes the conventional associated actuator coil, pivot and control. The ramp faces 250, 254 are located within the outer perimeter of the disks 222 thereby taking up some of the potential data storage space of the disk surface. The actuator coil rotates the load beams 224 outward so that the contacting load portions of the beam 224 rides up the first inclined surface 250 separating the head assembly 230 from the disk 222. Further outward rotation of the load beam 224 causes the load beam to ride down the oppositely sloped outward ramp 254 to be captured on a flat surface 244 of the ramp assembly 42.
The system of '549 has similar characteristics of shock resistance, power supply and particulate considerations as Matsumoto '695 described above. Also, '549 has the disadvantageous loss of potential data storage area at the perimeter of the disks. In addition, higher loading/unloading friction forces are required for a given head to disk positioning spring torque, since the loading portions of the load beam 224 are located nearer the midpoint of the beam than the head end. This translates into increased power, size and weight for the drive components and decreased battery life for portable drives.
Patent '374 by Anderson et al., describes a radially directed head loading apparatus 10 having an electrically controlled linear actuator 23, carrying a support arm 26 for positioning a Whitney-type suspension arm 28 and Whitney-size head 36. The suspension 28 creates a resilient, spring-like attribute to support the head 36 in read/write relationship to a disk 18 in normal operation.
A triangular, two sided, longitudinal ramp portion 44 is disposed along one face of the arm 28, and rides on a stationary circular cam 50. The ramp portion 44 is comprised of a first section 46 and a second section 48. The two sections are inclined and positioned with respect to the arm 28 and cam 50 so that the head 36 will gently approach and retreat vertically from the disk 18 as the arm 28 is actuated toward and away from the center of the disk 18 between normal operation and non-operation.
No discussion is provided on how the actuator 23 is secured during power off or inactive conditions to prevent the arm from projecting the head into a possible head-disk contact situation. For multiple head/disk systems, the size, cost and weight of multiple linear actuators with the associated power and thermal dissipation requirements may be problematic.
Patent '457 by Kahn also discloses a radially directed linear actuator arm 14 with a ramp 30 contacting a fixed cam 32 for vertically displacing a head 28 from a disk 26 during unloading. The method of securing the arm 14 in the unloaded position is not discussed.
Disk drive latching systems are known which add solenoids with actuating pins for capturing the head-positioning arm with the head or heads in a positive displaced position relative to the disk surface. Such solenoid capture systems contribute not only additional cost, weight, size, thermal dissipation, and decreased reliability added by another solenoid, but further decrease the potential battery life for portable systems.
The prior art systems that do incorporate latching mechanisms for restraining the head during power off or inactive state only partially address design issues related to the restraint problem. Except for stepper motor driven or positive solenoid latched systems, the robustness of restraint (i.e., shock resistance) scales with one or more of the critical design parameters. These cause data storage systems to be larger, weigh more, have lower reliability, and/or consume more power (lower battery life) than preferred.
What is needed, therefore, is a latching system which addresses the limitations of the prior art in an effective manner.